A systematic and comprehensive multiple-parameter analysis has been performed to define the optimal culture conditions for producing maximal amounts of the T-cell growth-promoting lymphokine interleukin-2 (IL-2) from primary cultures of lymphocytes freshly isolated from the blood, tonsil, spleen and thymus of different human subjects as well as from long-term cultures of T cells of lines initiated from patients with leukemia or lymphoma. The IL-2 production procedure that has proven most useful is a two-phase culture system in which pooled blood lymphocytes of healthy donors are cultivated for 4 days in spinner bottles prior to polyclonal activation for 24 hours in a serum-free medium with phytohemagglutinin, phorbol ester and B cells of Epstein-Barr virus-transformed human lymphoblastoid cell lines. IL-2 generated in more than 150 large-volume lots has been successfully utilized for functional and phenotypic studies in which 70 long-term (greater than 100 days) IL-2-dependent T-cell lines were established from 50 different donors. More recently, we have developed a simple, efficient, rapid and inexpensive procedure for the isolation and partial purification of IL-2. In this method, IL-2 is isolated by "pseudo-affinity" batch adsorption onto microparticular silicic acid, and then eluted using ethylene glycol in a phosphate-buffered high salt solution. A two-step purification scheme providing homogeneous IL-2 is anticipated when the silicic acid preparative procedure is used in conjugation with a subsequent method utilizing reverse phase high performance liquid chromatography or anti-IL-2 monoclonal antibody affinity chromatography. Immunoregulatory activity of IL-2 on T-cell-mediated tumor destruction is currently being defined using different in vivo murine models.